1. Field of the Invention
This invention relates generally to methods and devices for guiding pipe, and more particularly, but not by way of limitation, to improved methods and apparatus for vertically aligning and joining pipe section joints in a derrick.
2. Description of the Prior Art
In the drilling, completion and work-over of oil, gas and water wells, it is necessary to remove and install strings of pipe sections in a well bore. During such operations, a rig or derrick having a work floor or table and an elevator for vertically suspending one or more pipe sections above the work table is utilized. As pipe section joints are lowered into the well, additional pipe section joints are threaded to the upper end of the joint which extends a short distance above the work table. Generally, the pipe section which extends into the well bore is secured so that its upper-most threaded box end remains stationery during the threading process. The additional pipe section is then vertically suspended in the derrick by means of a carrying line, maneuvered, and rotated; threading its lower end to the upper threaded boxed end of the secured pipe joint.
In the past, it has been necessary to position a workman often called a stabber, in the upper sections of the derrick to maneuver the upper end of the to be threaded pipe section so that the maneuvered pipe is in alignment with the secured pipe in the well bore. Generally, this requires that the upper section of pipe rest on the lower section of pipe while the stabber maneuvers the pipe into alignment. After alignment is achieved a gripping device is attached to the lower end of the to be threaded pipe and this pipe is threaded to the pipe joint in the well bore.
A particular problem with this process of combining pipe joints is that the stabbing job is relatively dangerous. It requires a workman to be positioned in a high place in the derrick and to physically handle a heavy section of pipe. More importantly, this process also frequently damages the threads of the pipe as the sections are made up. Damage to the threads can occur either because the sections are not properly aligned when threaded due to errors on the part of the stabber or because the threads were initially misaligned yet connected prior to the stabber moving the pipe to an aligned position (and prior to the threading process). Furthermore, even if the stabber properly aligns the pipe, some pipe joints are sufficiently flexible that they bow during the alignment process. In this case, even if the stabber properly aligns the extreme end of the pipe, the lower threaded end of the pipe will not be properly aligned due to bowing.
Similar problems occur when pipe is being removed from the well. In the past, the derrick elevator has been used to raise pipe until a complete section of pipe is free and a second lower section of the pipe can be secured in the work table. A gripping device is then attached to a lower portion of the free section and this section is unthreaded from the secured section. A line attached to the upper end of the freed and unthreaded section is used to move this section to a stored position.
In this removal and disconnection process the pipe threads are often damaged because the threads of the free section rest on the threaded box end of the secured section as the pipe is canted by the line attached to its upper end and removed to a stored position. Tilting or canting of the free section on the secured section often crosses the threads prior to the separation. As with the joining process, the removal requires a stabber to perform a dangerous job of securing a line to and removing a very heavy piece of pipe.
In the past, various devices have been used for holding the lower end of a pipe section as it is threaded or unthreaded from the upper end of a pipe section secured in the work table. Examples of such devices are shown in U.S. Pat. Nos. 2,692,059; 2,828,024; 2,829,783; and U.S.S.R. Patent No. 309,113. Each of the devices described in these patents and the processes used in positioning pipe with these devices have not been satisfactory. Particularly, these devices still require the use of a pipe stabber located in an upper portion of the derrick and thread damage still occurs due to misalignment of the pipe and cross-threading. Also, these devices are easily damaged and are not suitable for many jobs.
By the present invention an improved pipe guiding and aligning method and apparatus is provided for positioning and guiding the suspended pipe section as they are threaded and unthreaded.